[core] fix parse_via() parsing

Issue discovered during OpenSIPS Security Audit 2021,
	by Alfred Farrugia & Sandro Gauci (Enable Security)

GHSA-wxfg-3gwh-rhvx
(cherry picked from commit ab611f7)

parser/parse_via.c

@@ -1804,7 +1804,6 @@ char* parse_via(char* buffer, char* end, struct via_body *vbody)
 
 			case ':':
 				switch(state){
-					case F_HOST:
 					case F_IP6HOST:
 						state=P_IP6HOST;
 						break;