nf: IDLETIMER: Fix broken uid field in the msg

Create uid from kuid to fix the broken uid field
in the message notifications introduced in
Change-Id: I18fc73eada512e370d7ab24fc9f890845037b729,
Otherwise we run into following build error:
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  CC      net/netfilter/xt_IDLETIMER.o
net/netfilter/xt_IDLETIMER.c: In function ‘reset_timer’:
net/netfilter/xt_IDLETIMER.c:360:16: error: incompatible types when assigning to type ‘uid_t’ from type ‘kuid_t’
make[2]: *** [net/netfilter/xt_IDLETIMER.o] Error 1
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Signed-off-by: Amit Pundir <amit.pundir@linaro.org>