net: ipv4: relax AF_INET check in bind()

commit d0733d2e

 (Check for mistakenly passed in non-IPv4 address)
added regression on legacy apps that use bind() with AF_UNSPEC family.

Relax the check, but make sure the bind() is done on INADDR_ANY
addresses, as AF_UNSPEC has probably no sane meaning for other
addresses.

Bugzilla reference : https://bugzilla.kernel.org/show_bug.cgi?id=42012

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-and-bisected-by: Rene Meier <r_meier@freenet.de>
CC: Marcus Meissner <meissner@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>