mgcp_e1: finish E1 support, add E1 support from libosmoabis

Currently only the endpoint handling for E1 exists, but there is no
actual code behind it that handles the E1 traffic.

Change-Id: I6b93809b5ac7d01af55888347dd787b0bc997ae1
Related: OS#2659
diff --git a/configure.ac b/configure.ac
index 7c63437..db44893 100644
--- a/configure.ac
+++ b/configure.ac
@@ -52,6 +52,8 @@
 PKG_CHECK_MODULES(LIBOSMOCTRL, libosmoctrl >= 1.1.0)
 PKG_CHECK_MODULES(LIBOSMOVTY, libosmovty >= 1.1.0)
 PKG_CHECK_MODULES(LIBOSMONETIF, libosmo-netif >= 0.6.0)
+PKG_CHECK_MODULES(LIBOSMOABIS, libosmoabis >= 0.6.0)
+PKG_CHECK_MODULES(LIBOSMOTRAU, libosmotrau >= 0.6.0)
 
 AC_ARG_ENABLE(sanitize,
 	[AS_HELP_STRING(