chan_pjsip: initial device state on endpoints is INVALID

When endpoints get loaded their device state gets set to 'INVALID' because the
channel driver has not been loaded yet.  Fixed by updating the device state for
every endpoint upon load of the channel driver.

(closes issue ASTERISK-23065)
Reported by: Rusty Newton
Review: https://reviewboard.asterisk.org/r/3123/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@405643 f38db490-d61c-443f-a65b-d21fe96a405b