syscalls/sighold02: ignore reserved signals

Some signals may be internally used by the C library. Do not attempt to
verify these.

Bug: 118442788
Signed-off-by: Steve Muckle <smuckle@google.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
(cherry picked from commit 158f68e5)
Bug: 122314690
Test: run vts-kernel -m VtsKernelLtp -t syscalls.sighold02
Merged-In: I47c808b3c386d54c8f70e443d41b062c1ee86ec9
Change-Id: I47c808b3c386d54c8f70e443d41b062c1ee86ec9