wiphy: Fix buffer overflow due to off-by-one error

Since channels numbers are used as indexes into the array, and given
that channel numbers start at '1' instead of 0, make sure to allocate a
buffer large enough to not overflow when the max channel number for a
given band is accessed.

src/manager.c:manager_wiphy_dump_callback() New wiphy phy1 added (1)
==22290== Invalid write of size 2
==22290==    at 0x4624B2: nl80211_parse_supported_frequencies (nl80211util.c:570)
==22290==    by 0x417CA5: parse_supported_bands (wiphy.c:1636)
==22290==    by 0x418594: wiphy_parse_attributes (wiphy.c:1805)
==22290==    by 0x418E20: wiphy_update_from_genl (wiphy.c:1991)
==22290==    by 0x464589: manager_wiphy_dump_callback (manager.c:564)
==22290==    by 0x4CBDDA: process_unicast (genl.c:944)
==22290==    by 0x4CC19C: received_data (genl.c:1056)
==22290==    by 0x4C7140: io_callback (io.c:120)
==22290==    by 0x4C5A97: l_main_iterate (main.c:476)
==22290==    by 0x4C5BDC: l_main_run (main.c:523)
==22290==    by 0x4C5F0F: l_main_run_with_signal (main.c:645)
==22290==    by 0x40503B: main (main.c:600)
==22290==  Address 0x4aa76ec is 0 bytes after a block of size 28 alloc'd
==22290==    at 0x48417B5: malloc (vg_replace_malloc.c:393)
==22290==    by 0x4BC4D1: l_malloc (util.c:62)
==22290==    by 0x417BE4: parse_supported_bands (wiphy.c:1619)
==22290==    by 0x418594: wiphy_parse_attributes (wiphy.c:1805)
==22290==    by 0x418E20: wiphy_update_from_genl (wiphy.c:1991)
==22290==    by 0x464589: manager_wiphy_dump_callback (manager.c:564)
==22290==    by 0x4CBDDA: process_unicast (genl.c:944)
==22290==    by 0x4CC19C: received_data (genl.c:1056)
==22290==    by 0x4C7140: io_callback (io.c:120)
==22290==    by 0x4C5A97: l_main_iterate (main.c:476)
==22290==    by 0x4C5BDC: l_main_run (main.c:523)
==22290==    by 0x4C5F0F: l_main_run_with_signal (main.c:645)
==22290==

src/wiphy.c

@@ -1616,8 +1616,12 @@ static void parse_supported_bands(struct wiphy *wiphy,
 				continue;
 
 			band->freq = freq;
+			/*
+			 * Since channels start at 1, allocate one extra in
+			 * order to use channel indexes without arithmetic
+			 */
 			band->freq_attrs = l_new(struct band_freq_attrs,
-							num_channels);
+							num_channels + 1);
 			band->freqs_len = num_channels;
 
 			/* Reset iter to beginning */