rtpengine: add mqtt dep

rtpengine will use the lib if found, so add it.
Signed-off-by: NSebastian Kemper <sebastian_ml@gmx.net>

net/rtpengine/Makefile

@@ -45,6 +45,7 @@ ENGINE_DEPENDS := \
 	+libevent2-pthreads \
 	+libhiredis \
 	+libip4tc \
+	+libmosquitto \
 	+libopenssl \
 	+libpcap \
 	+libpcre \