Add API pjsip_evsub_set_uas_timeout()

[ming]

A UAS which needs to recreate incoming subscriptions from a persistent
store can call pjsip_dlg_create_uas_and_inc_lock() and
pjsip_evsub_create_uas() as long as they've persisted the
correct data but since the timer is triggered by an incoming subscribe,
it's never set and the subscription never expires.

This ticket:

• Adds API pjsip_evsub_set_uas_timeout(), which is just a wrapper around evsub.c:set_timeout(sub, TIMER_TYPE_UAS_TIMEOUT, seconds)

• Also, fixed a copy-paste error in pjsip_sub_state_hdr_print() when printing retry-after parameter.

Thanks to George Joseph for the patch.

[ming]

In 5558:

Closed #1998: Add API pjsip_evsub_set_uas_timeout()