map: fix translation of icmp4 error messages

ICMP error messages are translated to ICMPv6 error messages with
erroneous destination address in the outer IPv6 header because sender
port is used instead of receiver port.

Both source and destination addresses in the inner IPv6 header are
translated erroneously because source and destination addresses of the
inner IPv4 header are getting zeroed during the translation.

With this commit, use receiver port for translation and save addresses
of the inner IPv4 header before translation of the inner header.

Type: fix

Change-Id: I1e93d54c1bbc154b401adcbb0fb661299655d01a
Signed-off-by: Alexander Chernavin <achernavin@netgate.com>