libuafs: include com_err.h in ukernel_swig.i

libuafs: include com_err.h in ukernel_swig.i

clang-16 is flagging an implicit-function-definition which results in a
build error when --enable-warning is turned on.

    PERLUAFS/ukernel_swig_perl.c:1585:9: error: call to undeclared
        function 'afs_com_err'; ISO C99 and later do not support
        implicit function declarations [-Wimplicit-function-declaration]
      afs_com_err("AFS::ukernel", code, "parsing line: '%s'", line);
      ^

Add an include for afs/com_err.h to resolve the warning.

Change-Id: Id02d8a3f0ec6d7d3a9f5ffe7fcacf1a6972700a0
Reviewed-on: https://gerrit.openafs.org/15179
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>