IB/srp: Use %pIS instead of inet_ntop()

Except for a minor log message change, this patch does not change
any functionality. For the introduction of %pIS, see also commit
10679643 ("lib: vsprintf: add IPv4/v6 generic %p[Ii]S[pfs]
format specifier").

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>