net: use sock_valbool_flag to set/clear SOCK_RXQ_OVFL

There's no point in open-coding sock_valbool_flag().

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>