MGCP_CONN_ID_MAXLEN actually includes a terminating nul, so we need to compare
strlen() against MGCP_CONN_ID_MAXLEN-1.
Log the length if it is too long.
Add MDCX_TOO_LONG_CI test to mgcp_test.c, testing a conn id of 33 characters.
Before this patch, the test returns error code 515 meaning "not found", while
now it returns 510 meaning "invalid", showing the off-by-one. Same is
illustrated by the error log ("not found" before, "too long" now), but the
error log is not verified by mgcp_test.c.
Change-Id: I8d6cc96be252bb486e94f343a8c7cae641ff9429
5336f57f05