NETFILTER: Kconfig: fix xt_physdev dependencies

xt_physdev depends on bridge netfilter, which is a boolean, but can still
be built modular because of special handling in the bridge makefile. Add
a dependency on BRIDGE to prevent XT_MATCH_PHYSDEV=y, BRIDGE=m.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>