Accumulate resolv.conf options

If there are multiple "options" lines, keep the options from all of
them.

Signed-off-by: Rob Murray <rob.murray@docker.com>

libnetwork/internal/resolvconf/resolvconf.go

@@ -480,10 +480,8 @@ func (rc *ResolvConf) processLine(line string) {
 		if len(fields) < 2 {
 			return
 		}
-		// Replace options from earlier directives.
-		// TODO(robmry) - preserving incorrect behaviour, options should accumulate.
-		//     rc.options = append(rc.options, fields[1:]...)
-		rc.options = fields[1:]
+		// Accumulate options.
+		rc.options = append(rc.options, fields[1:]...)
 	default:
 		// Copy anything that's not a recognised directive.
 		rc.other = append(rc.other, line)

libnetwork/resolvconf/resolvconf_unix_test.go

@@ -263,7 +263,7 @@ options opt1 opt2 opt3`,
 			input: `nameserver 1.2.3.4
 options opt1 opt2
 options opt3 opt4`,
-			result: []string{"opt3", "opt4"},
+			result: []string{"opt1", "opt2", "opt3", "opt4"},
 		},
 	} {
 		test := GetOptions([]byte(tc.input))