Add rwlock.h (and lock.h for that) to keep no-INET kernels compiling

after RADIX_NODE_HEAD_{,UN}LOCK() were added.  Must have been "learned"
by pollution before (most likely: route.h -> radix.h -> rwlock.h)

sys/net/if.c

@@ -50,6 +50,8 @@
 #include <sys/socketvar.h>
 #include <sys/protosw.h>
 #include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/rwlock.h>
 #include <sys/sockio.h>
 #include <sys/syslog.h>
 #include <sys/sysctl.h>