res_pjsip: Added "subscribe_context" to endpoint

If specified, incoming SUBSCRIBE requests will be searched for the matching
extension in the indicated context. If no "subscribe_context" is specified,
then the "context" setting is used.

ASTERISK-25471 #close

Change-Id: I3fb7a15f5bc154079bd348c08b7ad1cdd2d5e514

contrib/ast-db-manage/config/versions/9deac0ae4717_pjsip_add_subscribe_context.py

@@ -0,0 +1,21 @@
+"""pjsip_add_subscribe_context
+
+Revision ID: 9deac0ae4717
+Revises: ef7efc2d3964
+Create Date: 2016-07-04 12:11:28.117788
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '9deac0ae4717'
+down_revision = 'ef7efc2d3964'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    op.add_column('ps_endpoints', sa.Column('subscribe_context', sa.String(40)))
+
+def downgrade():
+    op.drop_column('ps_endpoints', 'subscribe_context')