net: fix net/core/sock.c build error

Fix net/core/sock.c build error when CONFIG_INET is not enabled:

net/built-in.o: In function `sock_edemux':
(.text+0xd396): undefined reference to `inet_twsk_put'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David S. Miller <davem@davemloft.net>