Merge uipc_bind() with unp_bind(). Unlike other unp_*() functions,

Merge uipc_bind() with unp_bind(). Unlike other unp_*() functions,
unp_bind() has the only uipc_bind() caller. In the uipc_usrreq() times,
it made sense to have dedicated unp_bind() for prevent tne code mess
within giant switch(), but now it doesn't.

ok bluhm@