USB gadget rndis: fix struct rndis_packet_msg_type unaligned bug

skb_push function may return a pointer which is not aligned as required
by struct rndis_packet_msg_type. Using attribute trick to fix this bug.

Signed-off-by: Roy Huang <roy.huang@analog.com>
Signed-off-by: Jie Zhang <jie.zhang@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>