logging.h: add L1 SAPI related context and filter

First user is osmo-bts in I6b7bb2e1d61502b61214f854a4ec5cbb7267545b.

Related: OS#2356
Change-Id: I814cb3328d99faca9220adb5a80ffb934f219d7d
diff --git a/include/osmocom/core/logging.h b/include/osmocom/core/logging.h
index 803b4a9..e56d3a5 100644
--- a/include/osmocom/core/logging.h
+++ b/include/osmocom/core/logging.h
@@ -154,6 +154,7 @@
 	LOG_CTX_GB_BVC,
 	LOG_CTX_BSC_SUBSCR,
 	LOG_CTX_VLR_SUBSCR,
+	LOG_CTX_L1_SAPI,
 	_LOG_CTX_COUNT
 };
 
@@ -166,6 +167,7 @@
 	LOG_FLT_GB_BVC,
 	LOG_FLT_BSC_SUBSCR,
 	LOG_FLT_VLR_SUBSCR,
+	LOG_FLT_L1_SAPI,
 	_LOG_FLT_COUNT
 };