configure.ac/debian: Require libosmo-mgcp-client-dev >= 1.2.0

We recently started to use some symbols that were not available in
libosmo-mgcp-client-dev 1.0.0 or even 1.1.0.  Let's depend on a newly
tagged version of libosmo-mgcp-client.

Change-Id: Ic5d3add1c69181aabbdb684a01a6ba7bcea1fe2c
2 files changed