core: dedicated function to check Via address with source ip

- received_via_test() as alternative to received_test() which looks also
  for rport and received parameters, confusing nat detection tests

(cherry picked from commit 194743bf0de92ae09fdc817e57863f6bdb159539)
nathelper: use dedicated function for testing via address against source ip

- reported by Igor Potjevlesch
- previous used functions was checking the presence of rport and
  received parameters, ending in a wrong result for nat testing

(cherry picked from commit 0b10377df11977d7ddd7e6bf30fe060d1fe200aa)
nat_traversal: use dedicated function for testing via address against source ip

(cherry picked from commit c6c4230fb0c4ca18f5c681c7195d3e1531255f3a)