rename mgcpgw_client_* to mgcp_client_*

The name "mgcpgw_client" referred to an MGCP gateway, which is rather an MGW
(Media Gateway). But this client code is more generally a client for the MGCP
protocol, independently from what the server program is called.

Rename the files as well as the function prefixes to drop the "gw". It is
purely cosmetic and not strictly necessary, but a good point in time for fixes
like this.

osmo-msc build will be adjusted by I093ad02ca0e532f659447c785e09678b3e6f220d.
osmo-bsc build will be adjusted by I6402c7cbe58dacae7630f7f03819f8102e54c699.
These should be applied right after this here is merged to avoid fallout.

Change-Id: I99f7faab637cfcc22ece64a1dbcbe590f2042187
diff --git a/tests/testsuite.at b/tests/testsuite.at
index 37347b3..4f4a303 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -14,9 +14,9 @@
 AT_CHECK([$abs_top_builddir/tests/legacy_mgcp/mgcp_transcoding_test], [], [expout], [ignore])
 AT_CLEANUP
 
-AT_SETUP([mgcpgw_client])
-AT_KEYWORDS([mgcpgw_client])
-cat $abs_srcdir/mgcp_client/mgcpgw_client_test.ok > expout
-cat $abs_srcdir/mgcp_client/mgcpgw_client_test.err > experr
-AT_CHECK([$abs_top_builddir/tests/mgcp_client/mgcpgw_client_test], [], [expout], [experr])
+AT_SETUP([mgcp_client])
+AT_KEYWORDS([mgcp_client])
+cat $abs_srcdir/mgcp_client/mgcp_client_test.ok > expout
+cat $abs_srcdir/mgcp_client/mgcp_client_test.err > experr
+AT_CHECK([$abs_top_builddir/tests/mgcp_client/mgcp_client_test], [], [expout], [experr])
 AT_CLEANUP