Log Message:
net/mosquitto: gc support for NetBSD before 6

mosquitto uses strnlen, which is required by POSIX.1-2008, but did not
appear in NetBSD before 6.  Because NetBSD 5 is ancient, and much
older than 8, the oldest version formally supported, drop the patch as
costing more in cognitive load than it helps, guessing there are zero
people benefiting