mgcp_msg: We must parse endpoint numbers as hex, not decimal!

The MGCP client uses hex numbers, while the server side parses it
as decimal. This results in the first 10 calls succeeding, but from
0x0a onwards it of course fails :/

Change-Id: I006f5f5325f0a5069d02fec8912a38d943cfc552
Closes: OS#2784
1 file changed