MFC r318255:

Add missing braces around MCAST_EXCLUDE check when KTR support is
compiled into the kernel

This ensures that .iss_asm (the number of ASM listeners) isn't incorrectly
decremented for MLD-layer source datagrams when inspecting im*s_st[1]
(the second state in the structure).

PR: 217509 [1]

MFC r281380:
Fix the IPV6_MULTICAST_IF sockopt handling. RFC 3493 says when the
interface index is specified as zero, the system should select the
interface to use for outgoing multicast packets. Even the comment
for the in6p_set_multicast_if() function says about index of zero.
But in fact for zero index the function just returns EADDRNOTAVAIL.

I.e. if you first set some interface and then will try reset it
with zero ifindex, you will get EADDRNOTAVAIL.

Reset im6o_multicast_ifp to NULL when interface index specified as
zero. Also return EINVAL in case when ifnet_byindex() returns NULL.
This will be the same behaviour as when ifindex is bigger than
V_if_index. And return EADDRNOTAVAIL only when interface is not
multicast capable.

MFC r273855:
Fix mbuf leak in IPv6 multicast code.
When multicast capable interface goes away, it leaves multicast groups,
this leads to generate MLD reports, but MLD code does deffered send and
MLD reports are queued in the in6_multi's in6m_scq ifq. The problem is
that in6_multi structures are freed when interface leaves multicast groups
and thread that does deffered send will not take these queued packets.

PR: 194577

MFC r273857:
Move ifq drain into in6m_purge().

Suggested by: bms

Sponsored by: Yandex LLC

MFC r262351:

Remove KASSERT from in6p_lookup_mcast_ifp().

When the devel/jenkins port, version 1.551 was started,
the kernel would panic if INVARIANTS was enabled in the kernel config.

Suggested by: bms

Approved by: re (gjb)

MFC r259884:

Correct warnings comparing unsigned variables < 0 constantly reported
while building kernels. All instances removed are indeed unsigned so
the expressions could not be true.

MFC r264364:
Properly release the in6_multi lock.

Sponsored by: Yandex LLC

MFC r259840:

In sys/netinet6/in6_mcast.c, in6m_is_ifp_detached() is only used
whenever KTR is defined, so put it between #ifdef KTR guards. This
avoids a warning about a unused function if KTR is not enabled.

MFC r281380:
Fix the IPV6_MULTICAST_IF sockopt handling. RFC 3493 says when the
interface index is specified as zero, the system should select the
interface to use for outgoing multicast packets. Even the comment
for the in6p_set_multicast_if() function says about index of zero.
But in fact for zero index the function just returns EADDRNOTAVAIL.

I.e. if you first set some interface and then will try reset it
with zero ifindex, you will get EADDRNOTAVAIL.

Reset im6o_multicast_ifp to NULL when interface index specified as
zero. Also return EINVAL in case when ifnet_byindex() returns NULL.
This will be the same behaviour as when ifindex is bigger than
V_if_index. And return EADDRNOTAVAIL only when interface is not
multicast capable.

MFC r273855:
Fix mbuf leak in IPv6 multicast code.
When multicast capable interface goes away, it leaves multicast groups,
this leads to generate MLD reports, but MLD code does deffered send and
MLD reports are queued in the in6_multi's in6m_scq ifq. The problem is
that in6_multi structures are freed when interface leaves multicast groups
and thread that does deffered send will not take these queued packets.

PR: 194577

MFC r273857:
Move ifq drain into in6m_purge().

Suggested by: bms

Sponsored by: Yandex LLC

MFC r262351:

Remove KASSERT from in6p_lookup_mcast_ifp().

When the devel/jenkins port, version 1.551 was started,
the kernel would panic if INVARIANTS was enabled in the kernel config.

Suggested by: bms

Approved by: re (gjb)

MFC r259884:

Correct warnings comparing unsigned variables < 0 constantly reported
while building kernels. All instances removed are indeed unsigned so
the expressions could not be true.

MFC r264364:
Properly release the in6_multi lock.

Sponsored by: Yandex LLC

MFC r259840:

In sys/netinet6/in6_mcast.c, in6m_is_ifp_detached() is only used
whenever KTR is defined, so put it between #ifdef KTR guards. This
avoids a warning about a unused function if KTR is not enabled.