rxrpc: Clear socket error

When an ICMP or ICMPV6 error is received, the error will be attached
to the socket (sk_err) and the report function will get called.
Clear any pending error here by calling sock_error().

This would cause the following attempt to use the socket to fail with
the error code stored by the ICMP error, resulting in unexpected errors
with various side effects depending on the context.

Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Jonathan Billings <jsbillin@umich.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>