msc_mgcp: use more conceise error msg on truncation

When a truncation check (osmo_strlcpy()) fails handle_error()
is called with MGCP_ERR_NOMEM as cause code. Which finally
results in an "out of memory" message. MGCP_ERR_NOMEM is only
used for failed truncation checks, so it makes sense to choose
a message that describes the cause of the problem better.

- rename MGCP_ERR_NOMEM to MGCP_ERR_TOOLONG
- replace error message string

Change-Id: Ifedb85c1933a30b2aa491b495119919f45782e2c
1 file changed