MFC 57785538c6e0d7e8ca0f161ab95bae10fd304047 and

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)