[IPV4] Fix EPROTONOSUPPORT error in inet_create

There is a coding error in inet_create that causes it to always return
ESOCKTNOSUPPORT.  It should return EPROTONOSUPPORT when there are
protocols registered for a given socket type but none of them match
the requested protocol.

This is based on a patch by Jayachandran C.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>