net: remove "net:" prefix from error messages

The prefix was not uniformly applied and is probably better
left off for using with OpError.

Update #4856

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84660046

Author: cixtor

src/pkg/net/interface.go

@@ -7,11 +7,11 @@ package net
 import "errors"
 
 var (
-	errInvalidInterface         = errors.New("net: invalid interface")
-	errInvalidInterfaceIndex    = errors.New("net: invalid interface index")
-	errInvalidInterfaceName     = errors.New("net: invalid interface name")
-	errNoSuchInterface          = errors.New("net: no such interface")
-	errNoSuchMulticastInterface = errors.New("net: no such multicast interface")
+	errInvalidInterface         = errors.New("invalid network interface")
+	errInvalidInterfaceIndex    = errors.New("invalid network interface index")
+	errInvalidInterfaceName     = errors.New("invalid network interface name")
+	errNoSuchInterface          = errors.New("no such network interface")
+	errNoSuchMulticastInterface = errors.New("no such multicast network interface")
 )
 
 // Interface represents a mapping between network interface name

src/pkg/net/ipsock_plan9.go

@@ -60,12 +60,12 @@ func parsePlan9Addr(s string) (ip IP, iport int, err error) {
 	if i >= 0 {
 		addr = ParseIP(s[:i])
 		if addr == nil {
-			return nil, 0, errors.New("net: parsing IP failed")
+			return nil, 0, errors.New("parsing IP failed")
 		}
 	}
 	p, _, ok := dtoi(s[i+1:], 0)
 	if !ok {
-		return nil, 0, errors.New("net: parsing port failed")
+		return nil, 0, errors.New("parsing port failed")
 	}
 	if p < 0 || p > 0xFFFF {
 		return nil, 0, &AddrError{"invalid port", string(p)}

src/pkg/net/lookup_plan9.go

@@ -63,7 +63,7 @@ func queryCS1(net string, ip IP, port int) (clone, dest string, err error) {
 	}
 	f := getFields(lines[0])
 	if len(f) < 2 {
-		return "", "", errors.New("net: bad response from ndb/cs")
+		return "", "", errors.New("bad response from ndb/cs")
 	}
 	clone, dest = f[0], f[1]
 	return
@@ -199,7 +199,7 @@ func lookupCNAME(name string) (cname string, err error) {
 			return f[2] + ".", nil
 		}
 	}
-	return "", errors.New("net: bad response from ndb/dns")
+	return "", errors.New("bad response from ndb/dns")
 }
 
 func lookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {