irqbalance: upgrade to 1.6.0

Upgraded from 1.2.0 to 1.6.0 to pick up
all the latest fixes and improvements

irqbalance made glib2 mandatory since 1.3.0, but is
using very little of it. glib2 linked statically
to minimize the impact.

1.2.0 size: 33,619
1.6.0 size: 99,539

~# irqbalance --version
	irqbalance version 1.6.0

~# ldd /usr/sbin/irqbalance
	/lib/ld-musl-armhf.so.1 (0xb6f5f000)
	libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xb6f43000)
	libc.so => /lib/ld-musl-armhf.so.1 (0xb6f5f000)

~# opkg info irqbalance
	Package: irqbalance
	Version: 1.6.0-6
	Depends: libc
	Status: install user installed
	Architecture: arm_cortex-a7_neon-vfpv4
	Installed-Time: 1582839249

Compile-tested: ipq806x/R7800 & ipq40xx/GL-B1300
Run-tested:     ipq806x/R7800 & ipq40xx/GL-B1300

Signed-off-by: Marc Benoit <marcb62185@gmail.com>