tipc: remove two indentation levels in tipc_recv_msg routine

The message dispatching part of tipc_recv_msg() is wrapped layers of
while/if/if/switch, causing out-of-control indentation and does not
look very good. We reduce two indentation levels by separating the
message dispatching from the blocks that checks link state and
sequence numbers, allowing longer function and arg names to be
consistently indented without wrapping. Additionally we also rename
"cont" label to "discard" and add one new label called "unlock_discard"
to make code clearer. In all, these are cosmetic changes that do not
alter the operation of TIPC in any way.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Cc: David Laight <david.laight@aculab.com>
Cc: Andreas Bofjäll <andreas.bofjall@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>