dwatch(1): Separate default values so `-[BK] num' don't affect usage

If you were to pass an invalid option after -B num' or -K num' you
would see that the usage statement would show the value you passed
instead of the actual default.

Moving the default values to separate variables that are unaffected
by the options-parsing allows the usage statement to correctly show
the hard-coded default values if no flags are used.

Sponsored by: Smule, Inc.