debian/control + SPEC: Add missing build dependency to libosmo-abis

In I6b93809b5ac7d01af55888347dd787b0bc997ae1 we introduced E1 support
to osmo-mgw, but failed to add it to the build dependencies of the
Debian packages, making network:osmocmo:nightly builds fail.

Change-Id: I45717bda3ef7eba1ef59b993cc8a69bf2f92a29f
diff --git a/contrib/osmo-mgw.spec.in b/contrib/osmo-mgw.spec.in
index d24417e..a34a715 100644
--- a/contrib/osmo-mgw.spec.in
+++ b/contrib/osmo-mgw.spec.in
@@ -35,6 +35,7 @@
 BuildRequires:  pkgconfig(libosmogsm) >= 1.0.0
 BuildRequires:  pkgconfig(libosmovty) >= 1.0.0
 BuildRequires:  pkgconfig(libosmocoding) >= 1.0.0
+BuildRequires:  pkgconfig(libosmo-abis)
 %{?systemd_requires}
 
 %description
diff --git a/debian/control b/debian/control
index aeceeac..33a9650 100644
--- a/debian/control
+++ b/debian/control
@@ -8,6 +8,7 @@
                autotools-dev,
                libosmocore-dev,
                libosmo-netif-dev,
+               libosmo-abis-dev,
                osmo-gsm-manuals-dev
 Standards-Version: 3.9.8
 Vcs-Git: git://git.osmocom.org/osmo-mgw.git