util: Library routines for printing and scanning large hex integers.

util: Library routines for printing and scanning large hex integers.

Geneve options are variable length and up to 124 bytes long, which means
that they can't be easily manipulated by the integer string functions
like we do for other fields. This adds a few helper routines to make
these operations easier.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Andy Zhou <azhou@nicira.com>