Update linux's libpcap to 1.6.2

ping @gkristic - could you please verify this libpcap_linux.a does not introduce additional dependencies?

RHEL5 ships with glibc 2.5

$ objdump -T sample | grep GLIBC | grep -v "GLIBC_2\.2\."
0000000000000000      DF *UND*	0000000000000000  GLIBC_2.4   __stack_chk_fail
0000000000000000      DF *UND*	0000000000000000  GLIBC_2.3   getifaddrs
0000000000000000      DF *UND*	0000000000000000  GLIBC_2.3   freeifaddrs
0000000000000000      DF *UND*	0000000000000000  GLIBC_2.3.4 __fprintf_chk
0000000000000000      DF *UND*	0000000000000000  GLIBC_2.3   __ctype_b_loc

There's a 2nd lib, libpcap_linux_tpacket3... faster when there's a lot of activity, but adds ~1K context switches per second when mostly idle.