LU-15143 osd-ldiskfs: osd_declare_write() underestimates credits

LU-15143 osd-ldiskfs: osd_declare_write() underestimates credits

osd_declare_write() seems to underestimate journal credits for
the extent case. It does not properly account credits for
a new extent tree block. 3 credits (bitmap, gd, self) should be
accounted for a new data block and for a new extent tree block.

Change-Id: Iad463cac3a2a8c2b2a6b1a634e7502039bb1b7e5
HPE-bug-id: LUS-10514
Signed-off-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-on: https://review.whamcloud.com/45328
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Artem Blagodarenko <artem.blagodarenko@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>