bgpd: Fix work-quanta to be a reasonable value

bgpd: Fix work-quanta to be a reasonable value

The work-quanta that a user can specify is ~4billion.  If a user
specifies such a large value this translates into processing 4billion
outgoing packets before moving onto the next interface.  This makes
no sense.  Reduce the value of allowed work quanta's to be between
1 and 10000.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by: Don Slice <dslice@cumulusnetworks.com>
Reviewed-by: Daniel Walton <dwalton@cumulusnetworks.com>
Reviewed-by: Vivek Venkatraman <vivek@cumulusnetworks.com>