libpcap: Fix dependency definitions for libpcap

Commit 35dd53a9e132 ("librdmacm/libibverbs: Statically bound libbnxtre.so.1 to rping")
causes a build failure, since src.libnames.mk declares a depencency on
libbnxtre.so, but the libpcap Makefile and prebuild lib dependencies
were not updated accordingly. Fix the declarations.

Fixes: 35dd53a9e132 ("librdmacm/libibverbs: Statically bound libbnxtre.so.1 to rping")
Reviewed by: ssaxena
Differential Revision: https://reviews.freebsd.org/D54048

(cherry picked from commit 73e8fe62466a8ae5576473d9be4c6df9a6eedab0)