Returning more appropriate error code from tport_tbind(), too.
This patch fixes tracked bugs
#1485624 (nua not binding to 5060),
#1485625 (nua_create() fails if STUN init fails) and
#1485632 (ncorrect error message for nua bind error).
Nua now also binds both to NUTAG_URL and NUTAG_SIPS_URL() URIs, nua_create()
fails if binding either of them fails.

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