mgcp: Put local connection options into a struct

Currently the local connection options have been stored as a string.

This patch replaces this string by a struct (that still contains a
string) along with the parsed fields (only the packetization period
at the moment).

It also re-adds the calls to set_local_cx_options() to the
handle_create_con() and handle_modify_con() functions. Except for
the test program this has no side effects, since the LCO values
aren't used yet.
diff --git a/openbsc/tests/mgcp/mgcp_test.ok b/openbsc/tests/mgcp/mgcp_test.ok
index 509958a..24f9b33 100644
--- a/openbsc/tests/mgcp/mgcp_test.ok
+++ b/openbsc/tests/mgcp/mgcp_test.ok
@@ -17,19 +17,19 @@
 Testing MDCX2
 Testing CRCX
 Packet duration not set
-Requested packetization period not set
+Requested packetetization period: 20-20
 Testing MDCX3
 Packet duration not set
 Requested packetization period not set
 Testing MDCX4
 Packet duration not set
-Requested packetization period not set
+Requested packetetization period: 20-20
 Testing MDCX4_PT1
 Packet duration not set
-Requested packetization period not set
+Requested packetetization period: 20-40
 Testing MDCX4_PT2
 Packet duration not set
-Requested packetization period not set
+Requested packetetization period: 20-20
 Testing MDCX4_PT3
 Packet duration not set
 Requested packetization period not set