build: Skip compiling network.h and rtsp.h if networking is not enabled.

rtsp.h relies on network.h and the latter conditionally defines fallback OS
structures that rely on configure tests, which are only run if networking
is enabled.

libavformat/Makefile

@@ -349,6 +349,8 @@ OBJS-$(CONFIG_TCP_PROTOCOL)              += tcp.o
 OBJS-$(CONFIG_TLS_PROTOCOL)              += tls.o
 OBJS-$(CONFIG_UDP_PROTOCOL)              += udp.o
 
+SKIPHEADERS-$(CONFIG_NETWORK)            += network.h rtsp.h
+
 EXAMPLES  = metadata output
 TESTPROGS = seek
 TOOLS     = pktdumper probetest