net: bridge: remove ipv6 zero address check in mcast queries

commit 0fe5119e267f3e3d8ac206895f5922195ec55a8a upstream.

Recently a check was added which prevents marking of routers with zero
source address, but for IPv6 that cannot happen as the relevant RFCs
actually forbid such packets:
RFC 2710 (MLDv1):
"To be valid, the Query message MUST
 come from a link-local IPv6 Source Address, be at least 24 octets
 long, and have a correct MLD checksum."

Same goes for RFC 3810.

And also it can be seen as a requirement in ipv6_mc_check_mld_query()
which is used by the bridge to validate the message before processing
it. Thus any queries with :: source address won't be processed anyway.
So just remove the check for zero IPv6 source address from the query
processing function.

Fixes: 5a2de63fd1a5 ("bridge: do not add port to router list when receives query with source 0.0.0.0")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>