Revert "Issue #237 : Resolver uses nameserver commented out in /etc/resolv.conf"

This reverts commit b5fb1f44ed435fa25fe3de87c9b9ee6c0aad5125.

Issue #237 : Resolver uses nameserver commented out in /etc/resolv.conf

This /etc/resolv.conf:
# x

# nameserver 8.8.8.8

Still configured 8.8.8.8 as nameserver, because the comment detection in `ldns_resolver_new_frm_fp_l()` didn't anticipate empty lines before the comment.
This fix removed all comment handling from `ldns_resolver_new_frm_fp_l()`. Instead a new function is introduced `ldns_fget_token_l_resolv_conf()` that skips comments that start with '#' and ';'. The old `ldns_fget_token_l()` (that is used for zonefiles too) still accepts only ';' for comments.

ldns: Upgrade to 1.8.3.

Merge commit 'cf3e3d5bd0a1fae39c74c7db5a4e8b10732d0766'

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D40226

Upgrade LDNS to 1.7.0.

I've been holding back on this because 1.7.0 requires OpenSSL 1.1.0 or
newer for full DANE support. But we can't wait forever, and nothing in
base uses DANE anyway, so here we go.

ldns_axfr_abort is apparently an undocumented API function. Unstaticize
and add a prototype + documentation to the relevant header.

Upgrade to latest ldns (1.6.17) and unbound (1.4.22).

MFC after: 3 weeks

Upgrade to 1.6.16

Import LDNS and build it as an internal library.

ldns_axfr_abort is apparently an undocumented API function. Unstaticize
and add a prototype + documentation to the relevant header.