Add missing #includes.

According to POSIX, these two header files should be able to be included
by themselves, not depending on other headers. The <net/if.h> header
uses struct sockaddr when __BSD_VISIBLE=1, while <netinet/tcp.h> uses
integer datatypes (u_int32_t, u_short, etc).

MFC after:	2 months

sys/net/if.h

@@ -43,9 +43,11 @@
 /*
  * <net/if.h> does not depend on <sys/time.h> on most other systems.  This
  * helps userland compatibility.  (struct timeval ifi_lastchange)
+ * The same holds for <sys/socket.h>.  (struct sockaddr ifru_addr)
  */
 #ifndef _KERNEL
 #include <sys/time.h>
+#include <sys/socket.h>
 #endif
 
 struct ifnet;

sys/netinet/tcp.h

@@ -34,6 +34,7 @@
 #define _NETINET_TCP_H_
 
 #include <sys/cdefs.h>
+#include <sys/types.h>
 
 #if __BSD_VISIBLE