6lowpan: mac802154: fix coding style issues

This patch fixed the coding style issues reported by checkpatch.pl

following issues fixed:
	CHECK: Alignment should match open parenthesis
	WARNING: line over 80 characters
	CHECK: Blank lines aren't necessary before a close brace '}'
	WARNING: networking block comments don't use an empty /* line, use /* Comment...
	WARNING: Missing a blank line after declarations
	WARNING: networking block comments start with * on subsequent lines
	CHECK: braces {} should be used on all arms of this statement

Signed-off-by: Varka Bhadram <varkab@cdac.in>
Tested-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>