netfilter: nft_meta: skip EAGAIN if nft_meta_bridge is not a module

If it is a module, request this module. Otherwise, if it is compiled
built-in or not selected, skip this.

Fixes: 0ef1efd1 ("netfilter: nf_tables: force module load in case select_ops() returns -EAGAIN")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>