sig_pri.c: Pull the pri_dchannel() PRI_EVENT_RING case into its own function.

* Populate the CALLERID(ani2) value (and the special CALLINGANI2 channel
variable) with the ANI2 value in addition to the PRI specific ANI2 channel
variable.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@414050 f38db490-d61c-443f-a65b-d21fe96a405b