[SCSI] libfc: update fcp and exch stats

Updates newly added stats from fc_get_host_stats,
added new function fc_exch_update_stats to
update exches related stats from fc_exch.c
by going thru internal ema_list elements.

Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Acked-by : Robert Love <robert.w.love@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>