net: Convert int functions to bool

Global function ipv6_rcv_saddr_equal and static functions
ipv6_rcv_saddr_equal and ipv4_rcv_saddr_equal currently return int.

bool is slightly more descriptive for these functions so change
their return type from int to bool.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>