net/bridge: fix trivial sparse errors

net/bridge//br_stp_if.c:148:66: warning: conversion of
net/bridge//br_stp_if.c:148:66:     int to
net/bridge//br_stp_if.c:148:66:     int enum umh_wait

net/bridge//netfilter/ebtables.c:1150:30: warning: Using plain integer as NULL pointer

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>