libpcap: fix build for uclinux target

As usual, uclinux is also linux. Also, -lpthread is needed to link the canusb
test.

Fixes:
http://autobuild.buildroot.net/results/3af/3af796bc0eaa8563f0fd1dfce090083482fa57b9/



[Thomas: fix typo in SoB line inside the newly added patch.]

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>