freebsd_network: Initialize some variables.

The cases where these were uninitialized are panics, but
continuable panics, so it makes sense to initialize them anyway.

Spotted by Clang.

src/libs/compat/freebsd_network/compat/sys/mbuf-fbsd.h

@@ -156,7 +156,7 @@ m_extrefcnt(struct mbuf *m)
 static __inline int
 m_gettype(int size)
 {
-	int type;
+	int type = 0;
 
 	switch (size) {
 	case MCLBYTES:
@@ -185,7 +185,7 @@ m_gettype(int size)
 static __inline void
 m_cljset(struct mbuf *m, void *cl, int type)
 {
-	int size;
+	int size = 0;
 
 	switch (type) {
 	case EXT_CLUSTER: