mgcp_client: fix error handling in mgcp message generation

The functions add_lco and add_sdp assert when the codec string can not
be generated. This is the case when an unexpected codec is addressed in
the input parameter mgcp_msg for mgcp_msg_gen(). Even though the API
user is expected only to use the codec identifiers in mgcp_client.h the
check should not be done with an assert. Instead mgcp_msg_gen() should
just return NULL imediately.

Also all generation functions should not use magic numbers as return
codes. Instead constants from errno.h should be used. It is also
problematic that the return codes from msgb_printf are added up.
Depending. It makes more sense to use an OR operator since msgb_printf
only returns 0 or -EINVAL, so the end result will be -EINVAL if one or
more msgb_printf fail and not just a random negative value.

Change-Id: Ibb788343e0bec9c0eaf33e6e4727d4d36c100017
Related: OS#5119
2 files changed