res_pjsip_endpoint_identifier_ip: Add support for SRV lookups.

This change implements SRV support for the IP based endpoint
identifier module. All possible addresses through SRV are looked
up and added as matches. If no SRV records are available a
fallback to normal host resolution is done. If an IP address
is provided then no SRV lookup occurs.

This is configured using the "srv_lookups" option on the
identify section and defaults to "yes".

ASTERISK-26693

Change-Id: I6b641e275bf96629320efa8b479737062aed82ac

contrib/ast-db-manage/config/versions/28ab27a7826d_add_srv_lookups_to_identify.py

@@ -0,0 +1,31 @@
+"""add srv_lookups to identify
+
+Revision ID: 28ab27a7826d
+Revises: 4468b4a91372
+Create Date: 2017-01-06 14:53:38.829655
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '28ab27a7826d'
+down_revision = '4468b4a91372'
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import ENUM
+
+YESNO_NAME = 'yesno_values'
+YESNO_VALUES = ['yes', 'no']
+
+def upgrade():
+    ############################# Enums ##############################
+
+    # yesno_values have already been created, so use postgres enum object
+    # type to get around "already created" issue - works okay with mysql
+    yesno_values = ENUM(*YESNO_VALUES, name=YESNO_NAME, create_type=False)
+
+    op.add_column('ps_endpoint_id_ips', sa.Column('srv_lookups', yesno_values))
+
+
+def downgrade():
+    op.drop_column('ps_endpoint_id_ips', 'srv_lookups')