userns: Properly print bluetooth socket uids

With user namespace support enabled building bluetooth generated the warning.
net/bluetooth/af_bluetooth.c: In function ‘bt_seq_show’:
net/bluetooth/af_bluetooth.c:598:7: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 7 has type ‘kuid_t’ [-Wformat]

Convert sock_i_uid from a kuid_t to a uid_t before printing, to avoid
this problem.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Masatake YAMATO <yamato@redhat.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>