MFC 57785538c6e0d7e8ca0f161ab95bae10fd304047 and

1e811efbc591699b872bea42b9de419c373199df:

57785538c6e0d7e8ca0f161ab95bae10fd304047:

Simplify the FreeBSD check using FreeBSD compiler macro.

Rather than rely on FreeBSD_version, defined in sys/param.h, use
FreeBSD__ defined by the compiler.

Reported by: emaste
MFC after: 1 week

(cherry picked from commit 57785538c6e0d7e8ca0f161ab95bae10fd304047)

1e811efbc591699b872bea42b9de419c373199df:

Fix non-IPv6 build post 57785538c6e0d7e8ca0f161ab95bae10fd304047.

57785538c6e0d7e8ca0f161ab95bae10fd304047 change the test for FreeBSD
from FreeBSD_version to FreeBSD. However this test was performed
before sys/param.h was included, therefore FreeBSD_version was never
defined. As the test was never true opt_random_ip_id.h was never included.

Submitted by: bdragon
Reported by: bdragon

(cherry picked from commit 1e811efbc591699b872bea42b9de419c373199df)