tipc: refactor tipc_sk_bind() function

We refactor the tipc_sk_bind() function, so that the lock handling
is handled separately from the logics. We also move some sanity
tests to earlier in the call chain, to the function tipc_bind().

Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>