p54: enhance rssi->dBm database import

This patch fixes several shortcomings of the
previous implementation. Features of the
rewrite include:

 * handles undocumented "0x0000" word at the
   start of the frequency table.
   (Affected some early? DELL 1450 USB devices
    and my Symbol 5GHz miniPCI card.)

 * supports more than just one reference point
   per band. (Also needed for the Symbol card.)

 * ships with default values in case the eeprom
   data is damaged, absent or unsupported.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/p54/lmac.h b/drivers/net/wireless/p54/lmac.h
index 04b63ec..5ca117e 100644
--- a/drivers/net/wireless/p54/lmac.h
+++ b/drivers/net/wireless/p54/lmac.h
@@ -551,6 +551,7 @@
 /* eeprom */
 int p54_download_eeprom(struct p54_common *priv, void *buf,
 			u16 offset, u16 len);
+struct p54_rssi_db_entry *p54_rssi_find(struct p54_common *p, const u16 freq);
 
 /* utility */
 u8 *p54_find_ie(struct sk_buff *skb, u8 ie);