net: add pf_family_names[] for protocol family

Modify the pr_info content from int to char * in sock_register() and
sock_unregister(), this looks more readable.

Fixed build error in ARCH=sparc64.

Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>