leaking_addresses: skip '/proc/1/syscall'

The pointers listed in /proc/1/syscall are user pointers, and negative
syscall args will show up like kernel addresses.

For example

/proc/31808/syscall: 0 0x3 0x55b107a38180 0x2000 0xffffffffffffffb0 \
0x55b107a302d0 0x55b107a38180 0x7fffa313b8e8 0x7ff098560d11

Skip parsing /proc/1/syscall

Suggested-by: Tycho Andersen <tycho@tycho.ws>
Signed-off-by: Tobin C. Harding <me@tobin.cc>