chan_sip: Case insensitive comparison of "defaultuser" parameter.

All the other configuration options are case insensitive, so this one
should be too.

ASTERISK-24355 #close
Reported by: HZMI8gkCvPpom0tM
patches:
  ast.patch uploaded by HZMI8gkCvPpom0tM (License 6658)
........

Merged revisions 430993 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 430994 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430995 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -30596,7 +30596,7 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 				if (peer->callingpres == -1) {
 					peer->callingpres = atoi(v->value);
 				}
-			} else if (!strcasecmp(v->name, "username") || !strcmp(v->name, "defaultuser")) {	/* "username" is deprecated */
+			} else if (!strcasecmp(v->name, "username") || !strcasecmp(v->name, "defaultuser")) {	/* "username" is deprecated */
 				ast_string_field_set(peer, username, v->value);
 				if (!strcasecmp(v->name, "username")) {
 					if (deprecation_warning) {