perf beauty socket: Rename header_dir to uapi_header_dir

Paving the way to pass more headers to be consumed, like
tools/perf/trace/beauty/include/linux/socket.h in addition to the
current tools/include/uapi/linux/in.h, to get the SOL_* defines.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/trace/beauty/socket.sh

 #!/bin/sh
 # SPDX-License-Identifier: LGPL-2.1
 
-[ $# -eq 1 ] && header_dir=$1 || header_dir=tools/include/uapi/linux/
+[ $# -eq 1 ] && uapi_header_dir=$1 || uapi_header_dir=tools/include/uapi/linux/
 
 printf "static const char *socket_ipproto[] = {\n"
 regex='^[[:space:]]+IPPROTO_(\w+)[[:space:]]+=[[:space:]]+([[:digit:]]+),.*'
 
-egrep $regex ${header_dir}/in.h | \
+egrep $regex ${uapi_header_dir}/in.h | \
 	sed -r "s/$regex/\2 \1/g"	| \
 	sort | xargs printf "\t[%s] = \"%s\",\n"
 printf "};\n"