[util] Mark srtp.h as an SSL header file

This CL adds srtp.h to the list of SSLHeaderFiles, in order to move it
from ssl_h_files to crypto_h_files. The header file only includes an
inclusion of ssl.h. ssl_h_files can depend on crypt_h_files but not the
other way around.

Change-Id: If7410624a8b2bbbd5afb7f66ec6f491968faf24e
Reviewed-on: https://boringssl-review.googlesource.com/c/32505
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

util/generate_build_files.py

diff --git a/util/generate_build_files.py b/util/generate_build_files.py
index 11b9a8a..9c635dc 100644
--- a/util/generate_build_files.py
+++ b/util/generate_build_files.py
@@ -416,7 +416,7 @@
 
 
 def SSLHeaderFiles(path, dent, is_dir):
-  return dent in ['ssl.h', 'tls1.h', 'ssl23.h', 'ssl3.h', 'dtls1.h']
+  return dent in ['ssl.h', 'tls1.h', 'ssl23.h', 'ssl3.h', 'dtls1.h', 'srtp.h']
 
 
 def FindCFiles(directory, filter_func):