IB/mlx4: Fix corruption of RoCEv2 IPv4 GIDs

When using IPv4 addresses in RoCEv2, the GID format for the mapped
IPv4 address should be: ::ffff:<4-byte IPv4 address>.

In the cited commit, IPv4 mapped IPV6 addresses had the 3 upper dwords
zeroed out by memset, which resulted in deleting the ffff field.

However, since procedure ipv6_addr_v4mapped() already verifies that the
gid has format ::ffff:<ipv4 address>, no change is needed for the gid,
and the memset can simply be removed.

Fixes: 7e57b85c ("IB/mlx4: Add support for setting RoCEv2 gids in hardware")
Reviewed-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx4/main.c

@@ -219,8 +219,6 @@ static int mlx4_ib_update_gids_v1_v2(struct gid_entry *gids,
 			gid_tbl[i].version = 2;
 			if (!ipv6_addr_v4mapped((struct in6_addr *)&gids[i].gid))
 				gid_tbl[i].type = 1;
-			else
-				memset(&gid_tbl[i].gid, 0, 12);
 		}
 	}