net: extend sockaddr interface to the all address families

This CL extends existing sockaddr interface to accommodate not only
internet protocol family endpoint addressess but unix network family
endpoint addresses.

This is in preparation for runtime-integrated network pollster for BSD
variants.

Update #5199

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/11979043

src/pkg/net/ipsock_posix.go

@@ -120,15 +120,6 @@ func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) (family
 
 // Internet sockets (TCP, UDP, IP)
 
-// A sockaddr represents a TCP, UDP or IP network address that can
-// be converted into a syscall.Sockaddr.
-type sockaddr interface {
-	Addr
-	family() int
-	isWildcard() bool
-	sockaddr(family int) (syscall.Sockaddr, error)
-}
-
 func internetSocket(net string, laddr, raddr sockaddr, deadline time.Time, sotype, proto int, mode string, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
 	var la, ra syscall.Sockaddr
 	family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)

src/pkg/net/sock_posix.go

@@ -11,6 +11,16 @@ import (
 	"time"
 )
 
+// A sockaddr represents a TCP, UDP, IP network endpoint address that
+// can be converted into a syscall.Sockaddr.
+type sockaddr interface {
+	Addr
+	family() int
+	isWildcard() bool
+	sockaddr(family int) (syscall.Sockaddr, error)
+	toAddr() sockaddr
+}
+
 // Generic POSIX socket creation.
 func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr, deadline time.Time, toAddr func(syscall.Sockaddr) Addr) (fd *netFD, err error) {
 	s, err := sysSocket(f, t, p)