RDMA/srp: Accept again source addresses that do not have a port number

The function srp_parse_in() is used both for parsing source address
specifications and for target address specifications. Target addresses
must have a port number. Having to specify a port number for source
addresses is inconvenient. Make sure that srp_parse_in() supports again
parsing addresses with no port number.

Cc: <stable@vger.kernel.org>
Fixes: c62adb7d

 ("IB/srp: Fix IPv6 address parsing")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>