CID: 1214223-1214230 If sent an invalid registration authentication header with multiple params of the same name, then only use the first of the params instead of leaking memory

CID:1024250 Dereference before null check. CID:1024251 Dereference before null check, we don't need tto check these, as they are already used above in all cases

CID:1214196 Dereference null return value, if we hit this condition, something very bad has happened, we should never have the private not set if we get to the hangup hook, log error instead of crashing

CID:1214163 Unchecked return value, check return value of switch_ivr_play_file and bail out if it fails

Putting `net-snmp-config --cflags` into CFLAGS causes major pollution;
it overrides optimization and debugging levels, warnings, and more.
While normally we do want to automatically locate library headers,
there has to be a better way to do this.  libsnmp is normally in the
usual place and doesn't need special handling.  Perhaps people with
libsnmp in a weird place should just need to add the -I flag to their
CFLAGS before build.