inet: Fix missing return value in inet6_hash

inet: Fix missing return value in inet6_hash

As part of a series to implement faster SO_REUSEPORT lookups,
commit 086c653f5862 ("sock: struct proto hash function may error")
added return values to protocol hash functions and
commit 496611d7b5ea ("inet: create IPv6-equivalent inet_hash function")
implemented a new hash function for IPv6.  However, the latter does
not respect the former's convention.

This properly propagates the hash errors in the IPv6 case.

Fixes: 496611d7b5ea ("inet: create IPv6-equivalent inet_hash function")
Reported-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: Craig Gallek <[email protected]>
Acked-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: David S. Miller <[email protected]>