Move eid functions to utils.c, mark netsock.h deprecated

Move eid functions from netsock.c to utils.c.  These functions were
already published by utils.h.  Flag netsock.h as deprecated and switch
res_pjsip_session.h to use netsock2.h.  The only code that still uses
netsock.h is chan_iax2.

ASTERISK-23920 #close
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/3661/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@417167 65c4cc65-6c06-0410-ace0-fbb531ad65f3