uapi: ebtables: don't include linux/if.h

linux/if.h creates conflicts in userspace with net/if.h

By using it here we force userspace to use linux/if.h while
net/if.h may be needed.

Note that:

include/linux/netfilter_ipv4/ip_tables.h and
include/linux/netfilter_ipv6/ip6_tables.h

don't include linux/if.h and they also refer to IFNAMSIZ, so they are
expecting userspace to include use net/if.h from the client program.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>