tweak LOGHNB()

Add braces around context part.

In the HNBGW_Tests.ttcn output, I see this:

 DRUA DEBUG TTCN3 HNodeB transmitting RUA DirectTransfer

which reads like the hNodeB would transmit a RUA to us. Instead, this is
us sending RUA to the hNodeB, which is much clearer like this:

 DRUA DEBUG (TTCN3 HNodeB) transmitting RUA DirectTransfer

This matches the way we typically show context info in osmo logging.

Change-Id: If6f0c3ae81c737b7488fa93c435179dcf27a5c94

include/osmocom/hnbgw/hnbgw.h

@@ -24,7 +24,7 @@ enum {
 };
 
 #define LOGHNB(HNB_CTX, ss, lvl, fmt, args ...) \
-	LOGP(ss, lvl, "%s " fmt, hnb_context_name(HNB_CTX), ## args)
+	LOGP(ss, lvl, "(%s) " fmt, hnb_context_name(HNB_CTX), ## args)
 
 enum hnb_ctrl_node {
 	CTRL_NODE_HNB = _LAST_CTRL_NODE,