If there are any "old programs which incorrectly set this" left,
they will now fail with EAFNOSUPPORT.
This make in_pcbbind() consistent with in_pcbconnect() and the other
protocol families.
As per my PR [kern/4441], which has the comment:
Steven's "TCP/IP Illustrated, Volume 2", page 730, notes that
in_pcbbind() has the check which determines if sin_family == AF_INET
commented out, but the same check in in_pcbconnect() is still active.
b1026bf11c