Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use the canonical include name for snmpmod.h. The build infrastructure takes
already care to pick up the correct version of the file depending on how
we build.

The ticks delivered by the SNMP daemon are now 64-bit, so make our
local tick variable which is used to reduce the number of updates from
kernel structures and to ensure intra-PDU consistency also 64 bit.

Compare with 0 if comparing an integer, not with NULL.

Style: remove an empty line.

Replace all uses of the old netgraph constants NG_*LEN by the new
constants NG_*SIZ that include the trailing NUL byte. This change
is mostly mechanical except for the replacement of a couple of snprintf()
and sprintf() calls with strlcpy.

Add build infrastructure for libbsnmp and the modules. Add the
netgraph module for the SNMP daemon.