Import wireguard fixes from pfSense 2.5

Import wireguard fixes from pfSense 2.5

Merge the following fixes from https://github.com/pfsense/FreeBSD-src
 1940e7d3  Save	address	of ingress packets to allow wg to work on HA
 8f5531f1  Fix connection to IPv6 endpoint
 825ed9ee  Fix tcpdump for wg IPv6 rx tunnel traffic
 2ec232d3  Fix issue with replying to INITIATION messages in server mode
 ec77593a  Return immediately in wg_init if in DETACH'd state
 0f0dde6f  Remove unnecessary wg debug printf on transmit
 2766dc94  Detect and fix case in wg_init() where sockets weren't cleaned up
 b62cc7ac  Close the UDP tunnel sockets when the interface has been stopped

Reviewed by:	kevans
Obtained from:	pfSense 2.5
MFC after:	3 days
Relnotes:	yes
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D28962