package/snort: bump version to 2.9.15.1

Fixes:
 - http://autobuild.buildroot.net/results/17802b5ad87f494a86d158f2547e68edddcc0a68



  ../../src/util.h:377:21: error: static declaration of 'gettid' follows non-static declaration
   static inline pid_t gettid(void)
                       ^~~~~~
  In file included from .../host/aarch64-buildroot-linux-gnu/sysroot/usr/include/unistd.h:1170,
                   from .../host/aarch64-buildroot-linux-gnu/sysroot/usr/include/daq_common.h:25,
                   from .../host/aarch64-buildroot-linux-gnu/sysroot/usr/include/daq.h:26,
                   from ../../src/decode.h:48,
                   from ../../src/spo_plugbase.h:31,
                   from ../../src/snort.h:36,
                   from sfcontrol.c:37:
  .../host/aarch64-buildroot-linux-gnu/sysroot/usr/include/bits/unistd_ext.h:34:16: note: previous declaration of 'gettid' was here
   extern __pid_t gettid (void) __THROW;
                  ^~~~~~

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>