Fix return value confusion of sa_cmp() by renaming the function sa_equal().

Fix return value confusion of sa_cmp() by renaming the function sa_equal().

The code in get_alternate_addr() checked for sa_cmp() == 0 but actually
sa_cmp() returned 1 for equal addrs. So rename the function to sa_equal()
to make it clear that a true return value means equality.

Found by Asa Yeamans (enigma2e at rivin net)
OK tb@