iw: Add support for NL80211_ATTR_WIPHY_COVERAGE_CLASS

New nl80211 attribute NL80211_ATTR_WIPHY_COVERAGE_CLASS allows setting
IEEE 802.11 coverage class, which is then used by drivers to calculate
slot time and ACK timeout for long distance links.

Two iw parameters are added: 'coverage' sets the coverage class
directly, while 'distance' is more user-friendly, as it allows to set
just the link distance and let iw do the necessary calculation itself.

Signed-off-by: Lukas Turek <8an@praha12.net>
diff --git a/info.c b/info.c
index 69af216..1a1b588 100644
--- a/info.c
+++ b/info.c
@@ -156,6 +156,14 @@
 			printf("\tRTS threshold: %d\n", rts);
 	}
 
+	if (tb_msg[NL80211_ATTR_WIPHY_COVERAGE_CLASS]) {
+		unsigned char coverage;
+
+		coverage = nla_get_u8(tb_msg[NL80211_ATTR_WIPHY_COVERAGE_CLASS]);
+		/* See handle_distance() for an explanation where the '450' comes from */
+		printf("\tCoverage class: %d (up to %dm)\n", coverage, 450 * coverage);
+	}
+
 	if (!tb_msg[NL80211_ATTR_SUPPORTED_IFTYPES])
 		goto commands;