Optionally re-introduce bb_info_msg()

Between Busybox 1.24.2 and 1.25.0 the bb_info_msg() function was
eliminated and calls to it changed to be bb_error_msg(). The downside of
this is that daemons now log all messages to syslog at the LOG_ERR level
which makes it hard to filter errors from informational messages.

This change optionally re-introduces bb_info_msg(), controlled by a new
option FEATURE_SYSLOG_INFO, restores all the calls to bb_info_msg() that
were removed (only in applets that set logmode to LOGMODE_SYSLOG or
LOGMODE_BOTH), and also changes informational messages in ifplugd and
ntpd.

The code size change of this is as follows (using 'defconfig' on x86_64
with gcc 7.3.0-27ubuntu1~18.04)

function                                             old     new   delta
bb_info_msg                                            -     182    +182
bb_vinfo_msg                                           -      27     +27
static.log7                                          194     198      +4
log8                                                 190     191      +1
log5                                                 190     191      +1
crondlog                                              45       -     -45
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/0 up/down: 215/-45)           Total: 170 bytes

If you don't care about everything being logged at LOG_ERR level
then when FEATURE_SYSLOG_INFO is disabled Busybox actually gets smaller:

function                                             old     new   delta
static.log7                                          194     200      +6
log8                                                 190     193      +3
log5                                                 190     193      +3
syslog_level                                           1       -      -1
bb_verror_msg                                        583     581      -2
crondlog                                              45       -     -45
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 3/1 up/down: 12/-48)            Total: -36 bytes

Signed-off-by: James Byrne <james.byrne@origamienergy.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/networking/udhcp/d6_packet.c b/networking/udhcp/d6_packet.c
index 493943d72..01d1c930b 100644
--- a/networking/udhcp/d6_packet.c
+++ b/networking/udhcp/d6_packet.c
@@ -17,7 +17,7 @@ void FAST_FUNC d6_dump_packet(struct d6_packet *packet)
 	if (dhcp_verbose < 2)
 		return;
 
-	bb_error_msg(
+	bb_info_msg(
 		" xid %x"
 		, packet->d6_xid32
 	);
@@ -40,7 +40,7 @@ int FAST_FUNC d6_recv_kernel_packet(struct in6_addr *peer_ipv6
 	}
 
 	if (bytes < offsetof(struct d6_packet, d6_options)) {
-		bb_error_msg("packet with bad magic, ignoring");
+		bb_info_msg("packet with bad magic, ignoring");
 		return -2;
 	}
 	log1("received %s", "a packet");