bnxt_en: Read phy eeprom A2h address only when optical diagnostics is supported.

For SFP+ modules, 0xA2 page is available only when Diagnostic Monitoring
Type [Address A0h, Byte 92] is implemented. Extend bnxt_get_module_info(),
to read optical diagnostics support at offset 92(0x5c) and set eeprom_len
length to ETH_MODULE_SFF_8436_LEN (to exclude A2 page), if dianostics is
not supported.

Also in bnxt_get_module_info(), module id is read from offset 0x5e which
is not correct. It was working by accident, as offset was not effective
without setting enables flag in the firmware request. SFP module id is
present at location 0. Fix this by removing the offset and read it
from location 0.

Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>